Intravenous and arterial cannulas presently in use depend upon a visual observance of blood itself in the hub of the cannula (flashback chamber); After the needle has entered the vein or artery blood does flow through the length of the cannula and fills the flashback chamber in order to indicate that the cannula needle has entered the vessel. The blood according to this method is visible in the chamber after a period of time so the needle may puncture the second wall of the vessel before any sign appears. This may result in improper administration of medication, hemorrhaging, collapse of the vein or artery, or other similar complications.
One method of addressing this situation is disclosed in U.S. Pat. No. 5,030,207. According to that patent a device is provided for indicating when an intravenous needle has entered the vein through the use of a solid fiber optic mounted in the needle for showing visual instantaneous vein entry. The distal end of the fiber optic reflects color, such as red blood to the magnifying system at the rear or proximal end of the fiber optic. The user observes immediate vein entry without any blood flow or exposure to blood. That invention is complicated to manufacture, requires a certain amount of light to work properly, and also forces the user to look and focus at the proximal end of the cannula instead of the puncture point.
Another method of addressing the problem is U.S. Pat. No. 5,314,410 includes a colored flexible membrane disposed within the transparent body of a hypodermic needle that is stretched over the proximal end of the needle cannula. As the needle reaches the inside of the blood vessel, pressure within the vessel is transferred through the cannula to the membrane which moves or inflates indicating entry has been achieve. This device also forces the user to look and focus at the proximal end of the cannula instead of the puncture point.
Both above methods are widely used, however these are somewhat inconvenient to use as the person using the device must look at the device rather than the patient.
In all the above methods the device is part of the cannula in contrary to the present which can be connected to any commercial cannula.
It is thus the main object of the present invention to provide a device which is more reliable because it gives sound signal even at a very low pressure, so that the indication of vessel penetration is prompt. Moreover, with the use of this device the chance of double puncture of the blood vessel decreases.